aka Walking Corpse syndrome
rare mental disorder in which people hold a delusional belief that they are dead (either figuratively or literally), do not exist, are putrefying, or have lost their blood or internal organs. In rare instances, it can include delusions of immortality.
-Berrios G.E. and Luque R. (1995) Cotard Syndrome: clinical analysis of 100 cases. Acta Psychiatrica Scandinavica 91: 185-188
Those who suffer from this illness often deny that they exist or that a certain portion of their body exists.